Thermosetting, epoxy functional compositions are used to form tough, resilient, water-resistant structures such as molded articles, protective coatings, structural composites, adhesives, hardware, equipment housings and components, building components, vehicle components, furniture components, and the like. A typical composition incorporates one or more monomers, oligomers, and/or polymers that are polyfunctional with respect to epoxy functionality. The compositions are cured (e.g., polymerized and/or crosslinked) by chemical reaction with one or more suitable hardeners that are polyfunctional with respect to functionality that is co-reactive with epoxy functionality. Exemplary hardeners include materials that are polyfunctional with respect to at least primary and/or secondary amine and/or OH functionality. Tertiary amine functionality also may be present, although this tends to function mostly as a catalyst for the curing reaction.
According to one exemplary mode of use, epoxy functional compositions are used in coatings systems to protect a wide range of articles against moisture intrusion, corrosion, physical damage, bio-damage, and/or the like. For example, these coating systems are used to protect oil and gas pipelines. These pipelines include many components, particularly pipes, coupling structures, fasteners, and the like that are metallic, often being steel. Exemplary pipeline coatings desirably meet standards promulgated by the Canadian Standard Association (CSA), as these standards guide the pipeline industry on a global basis.
Fusion bonded epoxy (FBE) coatings have been an industrial standard for corrosion protection of oil and gas steel pipelines for more than 40 years. FBE powders are electrostatically sprayed on the heated steel components such as pipe at 220-240° C. The powder melts, fluidly coats the substrate, and then cures to adhere to the pipe surface. The FBE coating provides a primary defense against pipeline corrosion by limiting oxygen permeation. The FBE coating often is used in combination with cathodic protection (CP) that also prevents oxidation of steel by supplying electrons at the affected area. FBE coatings typically are applied either as a stand-alone coating or as a component of a multi-layer system to improve weatherability and the ability to withstand external damage during maintenance, transportation and installation. In multilayer coating systems, the FBE coating functions as a base coating or primer for the top coat(s). A popular multi-layer top coat system is a three layer polyolefin (3LPO) system that utilizes two layers of an adhesive tie layer and an outer HDPE top coat to cover the FBE primer.
The 3LPO system provides excellent coating performance, but nonetheless has drawbacks. As one serious drawback, a typical 3LPO coating is applied using extrusion. Extrusion is very expensive compared to other coating techniques such as spraying. Hence, 3LPO coatings involve substantial capital investment and are very expensive. It would be desirable to provide a coating alternative to the 3LPO system that can be applied using less expensive coating techniques while still meeting CSA standards.
Epoxy coating formulations are under investigation as alternatives to a 3LPO coating system. Investigators face many technical challenges. A first challenge involves providing epoxy formulations that can cure fast to meet throughput goals while still maintaining mechanical performance as demonstrated by tensile, modulus, gouge resistance, and 1 inch bar bending characteristics. While epoxy hardeners are uncovered that provide rapid curing, it is often found that rapid curing is obtained at too high a cost in terms of reduction in mechanical properties.
Epoxy coating formulations are often supplied in two parts so that the epoxy functional and hardener materials are kept separate until the time of use. This prevents the coating formulations from curing too soon. The volumetric ratio at which the separate parts are mixed is very important to ensure efficient mixing and compatibility with inexpensive coating techniques such as high pressure airless spraying. Mixing is more difficult if the ratio of the epoxy part to the hardener part (or vice versa) significantly deviates from unity. It has been found that hardeners that offer suitable mixing ratios may tend to react too slow with the epoxy functional materials. Pipe coatings that involve powder and/or liquid epoxy formulations are described in U.S. Pat. Nos. 7,670,683, 7,790,288, 6,224,710, and 5,300,336.